Angiotensin II increases the intracellular calcium activity in podocytes of the intact glomerulus

Background. Knowledge about biological functions of podocytes in the glomer ulus is limited because of its unique anatomical location. Here we introduc e a new method for measuring the intracellular calcium activity ([Ca2+](i)) in the podocyte in the intact glomerulus. Methods. With the help of fluore scence high-resolution digital imaging and a recently developed ultraviolet laser-scanning microscope, [Ca-2](i) was measured in fura-2-loaded glomeru li and single podocytes of intact microdissected rat glomeruli. Results. An giotensin II (Ang II) increased [Ca2+](i) reversibly in a biphasic and conc entration-dependent manner. In contrast to Ang II, bradykinin, thrombin, ar ginine vasopressin, and serotonin did not change [Ca2+](i) in the glomerulu s. At reduced extracellular Ca2+ activity, Ang II released [Ca2+](i) from i ntracellular stores, but the second phase, corresponding to a Ca2+ influx f rom the extracellular space, was absent. The L-type Ca2+ channel blocker ni cardipine did not influence the Ang II-mediated [Ca2+](i) increase, and an increase of the extracellular K+ concentration did not change [Ca2+]i in th e glomerulus. The angrotensin II type I(AT(1)) receptor antagonist losartan inhibited the Ang II-mediated [Ca2+](i) increase. Confocal [Ca2+](i) measu rements using fura-2 or fluo-3 or fluo-4 on the single cell level show that some of the Ang II-mediated [Ca2+](i) response originated from podocytes. Costaining with calcein allowed the identification of podocytes because of the characteristic morphology and location in relationship to the capillary network. Conclusions. These data suggest that podocytes in the intact glom erulus respond to Ang II with an increase of [Ca2+](i) via an AT1 receptor.